Week-4 Challenge WOT Condition Part-2

Aim: - To run the HEV Reference Application with WOT drive cycle with different parameters and comment on the results.

Objectives: -

1. What is the difference between mapped and dynamic model of engine, motor and generator? How can you change model type?
2. How does the model calculate miles per gallon? Which factors are considered to model fuel flow?
3. Run the HEV Reference Application with WOT drive cycle. Change the grade and wind velocity in the environment block. Comment on the results.
4. Keeping all other parameters same, compare the simulated results of hybrid and pure electric powertrains.

Study #1: -

Q1. What is the difference between mapped and dynamic model of engine, motor and generator? How can you change model type?

Powertrain Block set provides two types of combustion engine models: mapped and dynamic.

Mapped Engine: -

1. Mapped engines represent macro engine behaviour as a set of lookup tables (brake torque, fuel flow, air mass flow, exhaust temperature, efficiency, and emissions) as functions of commanded load and measured engine speed
2. Mapped engine models are suitable for analysis and design activities that do not require engine subsystem dynamic characteristics, for example, in engine and transmission powertrain matching analysis for fuel economy, emissions, and performance trade-offs.

Dynamic Engine: -

1. Dynamic engines decompose engine behaviour into individual component models that account for engine dynamics, most notably intake airflow and turbocharger dynamics.
2. Dynamic engine models are suitable for designing control, estimator, and diagnostic algorithms that depend on dynamic subsystem states, for example, in closed-loop AFR (Air-Fuel Ratio) control algorithm development.

We can switch between mapped and dynamic engines by following the below procedures:

1. Open the EV model in Simulink.
2. Enter the passenger car block by double clicking it.
3. Then go to Electric plant block.
4. Inside the motor block right-click to find the variant option.

Study #2: -

Q2. How does the model calculate miles per gallon? Which factors are considered to model fuel flow?

Miles per Gallon (MPG) & Miles per Gallon-equivalent (MPGe): -

For a conventional gasoline vehicle, the fuel efficiency is calculated via miles-per-gallon (MPG).However, fuel efficiency for hybrid models is calculated via miles-per-gallon equivalent (MPGe).MPG is the number of miles your car can drive per gallon of gas. Figuring out an MPGe rating is a little more complicated. Since engines that use an alternative source of fuel can’t be measured by liquid gallons of fuel, the MPGe rating is calculated by figuring out the number of miles a vehicle can go using the same energy content as a gallon of gas. The EPA calculates that 33.7 kilowatt-hours of electricity is the equivalent to one gallon of gas.

In case of our EV model, inside the visualization block we have another block named Performance Calculations.

If we get inside this block we find the actual (MPG) calculations

Here, three different inputs are taken into consideration:

1. Vehicle Speed
2. Fuel flow
3. Battery power

The vehicle speed input is in m/s which is converted into miles by multiplying with 0.000621371.

Similarly the kilogram of fuel is converted into cubic meter by multiplying by 1/(1000*0.739).

This cubic meter value is then converted into gallons by multiplying it with 264.172. The mile value and gallon value is used to find MPG of the vehicle.

Now the battery value is initially converted from watts to kwh by dividing with 1000 and then to gallon equivalent by again dividing it with 33.7 (since 33.7 kwh = 1 gallon).

Then divide the value by 3600 to get in per seconds and multiply by 0.00378541 to get the value in cubic meter per gallons.

Q3. Run the HEV Reference Application with WOT drive cycle. Change the grade and wind velocity in the environment block. Comment on the results.

Model: -

We have changed the drive cycle to Wide Open Throttle (WOT) with a sample time = 40 seconds.

We have also altered the “Environment” block and changed wind speed to 25 m/s & grade = 10.

The simulation was run for a time period of 40 seconds.

Input Parameters: -

Environment Blockset: -

Results: -

Conclusions:

Plot #1: Trace Velocity, Target, Actual:

Top Velocity achieved = 50.1 mph

Time taken to accelerate = 29.034 sec

Time taken to decelerate = 3.226 sec

Plot #2: Motor & Engine RPM:

Top motor rpm = 12550 rpm

Top engine rpm = 6188 rpm

Plot #3: Motor & Engine Torque:

Maximum motor torque = 50 N-m

Maximum engine torque = 205.3 N-m

Plot #4: Battery current:

The battery supply current is at its maximum value of 167 Ampere when full throttle is applied by the user. It reduces drastically to the value of negative 150 during deceleration of the vehicle.

Plot #5: Battery SOC:

The battery SOC falls from 60% to 40% during the acceleration period of vehicle and it increases slightly to 43% during deceleration due to regenerative braking.

Plot #6: Fuel Economy:

Maximum Fuel Economy achieved = 6.056

Q4. Keeping all other parameters same, compare the simulated results of hybrid and pure electric powertrains.

Simulated results of HEV: -

Simulated results of pure EV: -

All the input parameters are kept same:

Drive Cycle: - Wide Open Throttle (WOT)

Simulation Time: - 40 seconds

Grade: - 10

Wind Velocity: - 25 m/s

Conclusion: -

1. The top speed achieved by hybrid vehicle is more than that of pure EV.
2. The battery current capacity of pure EV is much higher compared to that of HEV since in EV battery is the only driving unit.
3. Higher fuel economy is achieved in case of pure EV.